Internet Engineering Task Force E. Marocco
Internet-Draft Telecom Italia
Intended status: Standards Track J. Seedorf
Expires: January 17, 2013 NEC
July 16, 2012
WebSocket-based server-to-client notifications for the Application-Layer
Traffic Optimization (ALTO) Protocol
draft-marocco-alto-ws-01
Abstract
The Application-Layer Traffic Optimization (ALTO) protocol is
designed to allow entities with knowledge about the network
infrastructure to export such information to applications that need
to choose one or more endpoints to connect to among large sets of
logically equivalent ones. The base protocol specification adopts a
simple pull-based model, according to which the client retrieves the
information encoded as JSON objects over HTTP directly from the
server.
This document proposes (for discussion) a mechanism for providing
server-initiated information update notifications through a
WebSocket-based ALTO protocol extension that easily integrates in the
basic protocol model.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 17, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
Marocco & Seedorf Expires January 17, 2013 [Page 1]
Internet-Draft WebSocket transport for ALTO July 2012
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 4
2. Overview of operations . . . . . . . . . . . . . . . . . . . . 4
3. Information Resource Directory (IRD) Extensions . . . . . . . . 5
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Client-to-server Version Indication . . . . . . . . . . . . . . 6
5. Partial Updates Encoding . . . . . . . . . . . . . . . . . . . 7
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
Marocco & Seedorf Expires January 17, 2013 [Page 2]
Internet-Draft WebSocket transport for ALTO July 2012
1. Introduction
The Application-Layer Traffic Optimization (ALTO) protocol
[I-D.ietf-alto-protocol] is designed to allow entities with knowledge
about the network infrastructure to export such information to
applications that need to choose one or more endpoints to connect to
among large sets of logically equivalent ones. The base protocol
specification adopts a simple pull-based model, according to which
the client retrieves the information encoded as JSON objects over
HTTP directly from the server.
Such a pull-based model is well suited for use cases where the
information does not change frequently, e.g. when it represents
network and cost maps intended to provide a hint to peer-to-peer
applications that have to perform initial peer selection (i.e. the
primary use case that motivated the specification of the ALTO
protocol). However, over the years several similar use cases have
emerged, most of them with more stringent requirements in terms of
information freshness. Those use cases could also simply and
effectively be addressed by the ALTO protocol, provided it features a
mechanism for clients to receive server-initiated information update
notifications. This document proposes (for discussion) a mechanism
for providing such notifications through a WebSocket-based [RFC6455]
extension that easily integrates in the basic ALTO protocol model.
The WebSocket protocol is only one option such an extension could be
based on. Many alternatives can of course be considered, based on
virtually any bi-directional protocol that provides some sort of
publish/subscribe framework. Among others, XMPP, BGP and SNMP have
been proposed and to some extent discussed in different contexts as a
basis for providing similar features. The strong points of the
WebSocket protocol in this context -- and thus the reason why the
extension proposed here is based on it -- include:
o WebSocket is explicitly intended to provide bi-directionality to
HTTP, the transport the ALTO protocol is based on. The main
implication of this fact is that both the HTTP client and server
libraries/frameworks that ALTO implementations are based on will
natively support it (or, since the technology is very new, soon
will);
o a resource representing an update notification service related to
a particular resource instance made available by an ALTO server
can simply be identified by a WebSocket URI and advertized in the
Information Resource Directory (IRD) just as any other regular
resource;
Marocco & Seedorf Expires January 17, 2013 [Page 3]
Internet-Draft WebSocket transport for ALTO July 2012
o a resource representing an update notification service can be
unambiguously defined through a MIME type, just as any other
regular resource;
o reuse of HTTP authentication.
o [TODO: Is Origin-based security of any use here?]
The most appropriate way for encoding partial updates of ALTO
information is an open issue itself, at the time of writing,
discussed in [I-D.schwan-alto-incr-updates].
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Overview of operations
When an ALTO client wants to retrieve a particular piece of
information made available by an ALTO server and then receive
notifications about each subsequent change, it achieves that in the
following steps:
1. retrieve the IRD of the ALTO service it is going to access;
2. find in the IRD the URI of the resource it is interested in,
identifying it through the associated content type (e.g.
application/alto-networkmap+json);
3. retrieve a copy of the resource it is interested in;
4. find in the IRD the WebSocket URI of the update notification
service associated to the specific resource just retrieved;
5. establish a WebSocket connection against the URI of the update
notification service;
6. indicate the version tag of the retrieved resource to the server;
7. process each subsequent updates received on the WebSocket
connection in order to keep the local representation of the
recource up-to-date.
Steps 1 to 3 are regular ALTO operations, as defined in
[I-D.ietf-alto-protocol]. The following section will discuss (and at
Marocco & Seedorf Expires January 17, 2013 [Page 4]
Internet-Draft WebSocket transport for ALTO July 2012
some point hopefully define) the missing pieces of specification
needed for performing the remaining steps, namely:
1. a mechanism for identifying the WebSocket URI of the update
notification service associated to a particular resource;
2. a mechanism for the client to tell the server the version of the
resource stored locally;
3. a mechanism for encoding information updates.
The mechanism discussed here is intended to allow steps from 4 to 7
to be executed at an arbitrarily later stage in respect to steps 1-3
(i.e. the mechanism needs to be able to update arbitrarily stale
resource representations).
3. Information Resource Directory (IRD) Extensions
[NOTE: strawman proposal.]
This document specifies the additional optional "updates" property
for top-level IRD entries. The new property is specifically defined
as:
updates A WebSocket URI as defined in [RFC6455] at which the ALTO
server provides dynamic updates of the corresponding resource.
3.1. Example
The following is an example Information Resource Directory returned
by an ALTO Server. In this example, the ALTO Server provides both a
network map and a cost map with corresponding update notification
services.
Marocco & Seedorf Expires January 17, 2013 [Page 5]
Internet-Draft WebSocket transport for ALTO July 2012
{
"resources" : [
.
.
.
{
"uri" : "http://alto.example.com/networkmap",
"media-types" : [ "application/alto-networkmap+json" ],
"updates" : "ws://alto.example.com/networkmap"
}, {
"uri" : "http://alto.example.com/costmap/num/routingcost",
"media-types" : [ "application/alto-costmap+json" ],
"capabilities" : {
"cost-modes" : [ "numerical" ],
"cost-types" : [ "routingcost" ]
},
"updates" : "ws://alto.example.com/costmap/num/routingcost"
}
]
}
4. Client-to-server Version Indication
As discussed in [I-D.schwan-alto-incr-updates], indication of the
version of the locally stored resource can happen in two ways:
o after the WebSocket connection has been established, with an ad-
hoc client-to-server signalling message such as:
{"reference-tag": "1266506140"}
The main drawback of such an approach consists with the added
complexity both on the client side and on the server side (e.g.
for handling error conditions, race conditions, etc.);
o in the WebSocket connection initiating GET request, by means of a
HTTP header field such as If-Modified-Since or If-None-Match. The
advantage of such an approach consists of the fact that the data
on the WebSocket connection flows on the server-to-client
direction only, adding no additional complexity to a client
already able to process partial updates. The drawback is that
none of the existing HTTP headers seem to have the exact required
semantic.
Marocco & Seedorf Expires January 17, 2013 [Page 6]
Internet-Draft WebSocket transport for ALTO July 2012
5. Partial Updates Encoding
Possible encoding options for partial updates are discussed in
[I-D.schwan-alto-incr-updates], for the case of client-initiated
transactions. The very same considerations also apply to the case of
server-initiated notifications. It seems therefore straightforward
to assume that the same encoding will be adopted here.
6. Example
[TODO: Illustrate a full example, from the IRD, the retrieval of the
resource and the establishment of the WS connection.]
7. Security Considerations
[TODO: A lot to be said here.]
8. Conclusion
This document discusses an extension to the ALTO protocol to allow
for server-initiated information update notifications. Specifically,
a WebSocket-based ALTO protocol extension is proposed that easily
integrates in the basic protocol model.
9. References
9.1. Normative References
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-12 (work in progress), July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, December 2011.
9.2. Informative References
[I-D.schwan-alto-incr-updates]
Schwan, N. and B. Roome, "ALTO Incremental Updates",
draft-schwan-alto-incr-updates-01 (work in progress),
March 2012.
Marocco & Seedorf Expires January 17, 2013 [Page 7]
Internet-Draft WebSocket transport for ALTO July 2012
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
Authors' Addresses
Enrico Marocco
Telecom Italia
Via Reiss Romoli, 274
Torino, 10148
Italy
Phone:
Email: enrico.marocco@telecomitalia.it
Jan Seedorf
NEC Laboratories Europe, NEC Europe Ltd.
Kurfuersten-Anlage 36
Heidelberg, 69115
Germany
Phone: +49 (0) 6221 4342 221
Email: jan.seedorf@neclab.eu
URI: http://www.neclab.eu
Marocco & Seedorf Expires January 17, 2013 [Page 8]